1. Field of the Invention
The present invention relates to a thin silicon wafer and a method of manufacturing the same, and more particularly, to a technique for polishing the rear surface of a silicon wafer, which is formed by a before process in a semiconductor device process, using a chemical mechanical polishing method for an after process in the semiconductor device process to give gettering capability to the thin silicon wafer.
Priority is claimed on Japanese Patent Application No. 2008-105781, filed Apr. 15, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
With the development of mobile phone and digital still camera techniques, the thickness of a semiconductor device package provided in the apparatus has been reduced.
Such a thin semiconductor device is manufactured by slicing a silicon single crystal pulled by, for example, a CZ (Czochralski) method into a silicon wafer and forming a circuit on the silicon wafer. When impurities, such as heavy metal, are mixed with the silicon wafer, the device characteristics significantly deteriorate.
It is certainly necessary to reduce the thickness of a device chip in order to reduce the thickness of the semiconductor device package.
However, there is a concern that impurities, such as heavy metal, will be mixed with a silicon wafer for an after process in a semiconductor device process, particularly, a thinning process of polishing the rear surface of the wafer to reduce the thickness of the wafer to about 50 μm. When impurities, such as heavy metal, are mixed with the silicon wafer, electrical characteristics of a device significantly deteriorate. Therefore, a technique for preventing the mixture of impurities, such as heavy metal, in the thinning process is needed.
In the related art, the following methods have been used to remove heavy metal from the silicon wafer: an IG (intrinsic gettering) method of forming an oxygen precipitate on a silicon wafer; and an EG (extrinsic gettering) method of forming a gettering site, such as backside damage, on the rear surface of a silicon wafer.
JP-A-6-338507 discloses a technique related to an IG process, and JP-A-2006-313922 discloses an example of the EG method (paragraph [0005]).
However, in the related art, the IG (intrinsic gettering) method is used in a process before the semiconductor device process (device manufacturing process), and requires a heat treatment temperature of 600° C. or more in order to remove heavy metal dispersed in the bulk of the silicon wafer. In general, during a thinning process, which is an after process in the semiconductor device process, the heat treatment temperature is equal to or lower than 400° C. Therefore, precipitation is not sufficiently performed, and it is difficult to sufficiently getter heavy metal.
In recent years, there has been a demand for a reduction in the thickness of a device. For example, the thickness of a device is reduced from 50 μm to 40 μm or less, for example, about 30 μm. When the thickness of the device is reduced to the above-mentioned range, most of the IG layer having a gettering effect is removed in the thinning process of the IG (intrinsic gettering) method according to the related art. Therefore, it is difficult to obtain sufficient gettering capability, which causes a defective device.
As such, it is difficult to use the gettering method, which is used in a before process in the semiconductor device process, in an after process in the semiconductor device process. Therefore, when heavy metal contamination occurs in the process after the semiconductor device process, it has a significantly adverse effect on the reliability test of a device after a molding process (product).